In the fluidized-bed treatment of metallic and non-metallic objects, it is a common practice to lower the objects through an upwardly open mouth of a fluidized-bed chamber into the fluidized bed turbulently maintained in this chamber, which can be of cylindrical or polygonal configuration, by introducing a fluidizing-gas, which can be air, through a nozzle plate at the bottom of this chamber.
The fluidized-bed chamber can thus have vertical chamber walls and a nozzle-plate or bottom formed with a number of gas outlet orifices and a plenum or distributing-compartment arrangement below this plate for feeding the fluidizing-gas to the orifices.
The chamber contains a fluidized bed of heat-carrying particles of a fine-grained material, e.g. ceramic or refractory substances which are fluidized by the gas which can be any treating gas.
The orifices can be discrete nozzle structures or porous plugs in appropriate openings, the different configurations of the orifices being utilized for different treatment processes and conditions.
Customarily this nozzle plate, which forms the floor of the chamber, is built into and is integral with the housing structure forming the chamber, e.g. by being welded to the side walls and any walls or the like forming the distributing compartments beneath this plate.
This causes problems when and if the nozzle plate must be replaced. This can occur when the nozzle assembly has a pressure drop which is greater than is desired for specific applications. The nozzle-plate must then be cut away from the chamber and a new nozzle-plate substituted and welded into place.
Naturally, this is a time-consuming and expensive procedure which limits the versatility of the fluidized-bed chamber because it makes it impractical to replace the nozzle-plate whenever changing conditions are confronted.
It should be appreciated that for certain treatments a stronger flow may be required in the center of the chamber than at the periphery or vice versa and, without the ability to readily replace the nozzle-plate, existing apparatus cannot be adapted to such changes in the desired operating conditions. Furthermore, prior art fluidized-bed chambers are characterized by nonhomogeneous boundary conditions in the fluidized-bed along the vertical walls of the chamber.